"We announce the reactivation of the Toubou Front for the Salvation of Libya (TFSL, an opposition group active under the former regime) to protect the Toubou people from ethnic cleansing," Issa Abdel Majid Mansur told AFP.
"If necessary, we will demand international intervention and work towards the creation of a state, as in South Sudan," he said after more than 10 people were reported killed in clashes in the southern oasis city of Sabha.
Monday's fighting pitted Toubou tribesmen and Sabha residents, Abdelrahman Seif al-Nasr, security chief of the southern Fezzan region, told AFP.
According to Ali al-Dib, a former rebel, the clashes erupted in the city centre and resulted in between 15 and 20 dead among the ex-rebel forces. Dib said the fighting broke out when the Toubou refused to hand over to local authorities one of their men accused of killing a member of the Bussif tribe.
Mansur, formerly an opposition activist against the regime of Moamer Kadhafi, had announced the dissolution of the TFSL movement after the slain dictator's regime fell.
"It turns out that the National Transitional Council and the Kadhafi regime are no different. The NTC has a programme to exterminate us," claimed Mansur, whose people played a key role in the south during last year's revolt.
"We have already said that the unity of Libya was above every other consideration. But now we have to protect both ourselves and other minorities," Mansur told AFP.
The Toubou are oasis farmers by tradition who also have connections beyond Libya's borders. They live in southern Libya, northern Chad and in Niger, and have on previous occasions denied having separatist ambitions.
Ruling NTC member Mukhtar al-Jadal said on Monday that NTC chief Mustafa Abdel Jalil had met representatives from the south in an effort to broker a solution to the crisis in Sabha.
A local source said Toubou tribesmen who had been in "brigades of former rebels have defected and rejoined their own" people, adding that "some elements from Chad are fighting with the Toubou."
The Toubou have also been involved in deadly clashes with another tribe in the Saharan oasis of Kufra, where two ethnic groups are locked in a standoff over smuggling.
Despite an army-brokered truce, tensions still simmer in Kufra, where clashes between the Toubou and the Zawiya and other groups claimed more than 100 lives during a fortnight of violence in February.
The triangle bordering Chad, Egypt and Sudan is a key transit route for the trafficking of goods of all kinds, both legal and contraband -- alcohol, cigarettes, counterfeit goods, drugs, weapons and especially illegal immigrants hoping to reach Europe.